Nanoscale ink-jet printing

ABSTRACT

A non-direct contact ink-jet style printer is disclosed herein, which uses a superfluid cryogenic fluid such as superfluid helium as the ink medium. Superfluid helium is non-viscous thus enabling the print head of the present invention to print nanoscale characters onto a substrate. In one exemplary embodiment, dopants are injected into the ink droplets to load the droplets with dopants, which then deliver the dopants onto the substrate. Multiple nozzles and different dopants may be used with the embodiments disclosed herein to provide different outputs on the substrate. Spent or un-used droplets and dopants may be educted away and discarded or scrubbed for reuse. Methods for printing using superfluid helium are also discussed herein.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of provisional application Ser. No.60/384,602, filed May 29, 2002, entitled NANOSCALE INK-JET PRINTING BYUSE OF SUPERFLUID LIQUID HELIUM JETS, the content of which is expresslyincorporated herein by reference.

Nanoscale printing is generally discussed herein with particulardiscussion on nanoscale printing using a cryogenic source as the mediumto deposit a dopant onto a substrate.

BACKGROUND

Existing methods for liquid deposition are either limited tomicron-scale resolution or larger or are slow and cumbersomedirect-contact techniques. One exemplary liquid deposition methodincludes ink-jet printing. Ink-jet printing is an accurate,high-throughput, non-contact technique that has been used with a widevariety of fluids ranging from printer ink to electrical solder topolymers to biologically active molecules. Since ink-jet printing isintrinsically droplet-based, it is very well suited to digital controland thereby to mask-free deposition. Being a non-contact technique, inkjet deposition is inherently contamination-free. However, due to basicphysical limitations, existing ink-jet printing is limited to featuresizes of about 15 μm or larger. Therefore, nanoscale printing, in theorder of 1 to 999 nanometers, using existing ink-jet technology is notpossible at least without sacrificing throughput.

Alternative writing techniques have emerged for depositing liquids atlinewidths down to about 100 nm. Principle among these is the “dip-pen”technique of Mirkin and co-workers, which developed the concept based onfluid flow through the meniscus formed when a fluid-coated atomic forcemicroscope (AFM) tip is brought into contact with (or near proximity to)a solid surface. However, dip-pen writing is inherently slow.

Dip-pen technique is capable of printing arrays as arrays of AFM tipscan be fabricated. However, the tip spacing is dictated by the width andlength of the AFM cantilevers, which typically is in the order of about50 μm tip-to-tip spacing between cantilevers of 300 μm length. Thesedimensions define the minimum grid size of the writing array, meaningthat each tip must still cover an area of at least 50 μm×300 μm.Moreover, there is significant overhead time required to reload theliquid coating on each tip when the “ink” is exhausted.

The dip-pen community is now attempting to incorporate ink reservoirsand microfluidic flow channels into the dip-pen microstructures in orderto continually supply fluid to each tip. Whether these efforts will besuccessful remains to be seen. In all events, dip-pen direct writing isa cumbersome approach in comparison to ink-jet printing. However, itdoes offer nanoscale resolution, which current ink-jet deposition doesnot.

Another printing technology is photolithographic process. Broadlyspeaking, it is a process by which an image is transferred from a maskto a wafer through the use of a photosensitive material often calledphotoresist. Through light-activated chemical reaction, a photoresist iseither process hardened or process softened. The process also involvesetching and baking to achieve the desired outcome. However, becauseetching and baking are involved, the process is generally notappropriate for depositing biologically active materials, such as DNA,diagnostic immunoassay, antibody and protein arrays.

Accordingly, there is a need for nanoscale printing capable of high rateand accuracy without the drawbacks of prior art printers. A highthroughput, non-contact, nanoscale printing technology would improveexisting fabrication technology by decreasing device structure sizesinto the nanoscale regime. In addition, a discrete droplet nanoscaleprinting technique would allow the use of single molecules asfundamental building blocks for fabrication, including both complexand/or biologically active molecules. Exemplary areas of technologicalrelevance include the deposition of biomolecules (e.g., proteins,peptides, DNA) in nanoarrays for biological sensor applications and thepatterned deposition of complex molecular species to form electronic andmechanical devices based on single molecules and/or on nanostructures ofmolecules.

SUMMARY

The present invention specifically addresses and alleviates theabove-mentioned deficiencies associated with the prior art assemblies.More particularly, the present invention may be implemented by using ajet apparatus for nanoscale printing onto a substrate comprising a printhead and a translational apparatus housed in a housing comprising atleast one housing chamber; a reservoir comprising a cryogenic fluid incommunication with the print head; and a dopant injector mechanicallycoupled to a storage containment comprising dopant molecules; andwherein at least one droplet of the cryogenic fluid is discharged fromthe print head and is expelled across at least a part of the housingchamber to combine with at least one dopant molecule discharged from thedopant injector, and wherein the combined at least one droplet of thecryogenic fluid and the at least one dopant molecule collides with thesubstrate positioned on the translational apparatus.

In another aspect of the present invention, a printer capable ofnon-contacting nanoscale printing is disclosed comprising a nozzlehaving a nanoscale diameter orifice, a cryostat comprising a chambercomprising superfluid helium in fluid communication with the print head,a housing comprising at least one chamber comprising dopant molecules;and a translational apparatus comprising a substrate; wherein thesuperfluid helium issuing from the nozzle of the print head breaks upinto nanoscale droplets; and wherein one or more nanoscale droplets ofsuperfluid helium each picks up at least one dopant molecule anddelivers the at least one dopant molecule into contact with thesubstrate.

In still yet another aspect of the present invention, a method isdisclosed for non-contact printing onto a substrate comprising the stepsof issuing a stream of superfluid helium from a nozzle along a path andallowing the stream to form into a plurality of nanoscale heliumdroplets; placing dopants in the path of the plurality of nanoscalehelium droplets and allowing at least some of the droplets to pick upsome of the dopants placed in the path of the droplets; and depositingthe picked up dopants by allowing the at least some of the droplets thatpicked up the dopants to collide with the substrate.

The present invention may also be implemented by incorporating a jetapparatus for nanoscale printing onto a substrate comprising a housingcomprising a nozzle having a nanoscale orifice, a chamber under avacuum, a translational apparatus comprising a substrate, and a cryostatcomprising a cryogenic source, wherein at least some of the cryogenicsource issues from the nozzle and disperses into nanoscale droplets inthe chamber, wherein at least some of the nanoscale droplets eachcomprises at least one dopant molecule picked up in the cryostat orpicked up in the chamber, and wherein the picked up nanoscale dropletsimpact with the substrate,

Other aspects and variations of the apparatus and method summarizedabove for nanoscale printing are also contemplated and will be morefully understood when considered with respect to the followingdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will be more fully understood when considered with respect tothe following detailed description, appended claims and accompanyingdrawings, wherein:

FIG. 1 is a semi-schematic component diagram depicting a continuous modesuperfluid liquid helium jet apparatus for nanoscale ink-jet depositionprovided in accordance with one aspect of the present invention; and

FIG. 2 is a block flow diagram of a control system of the jet apparatusof FIG. 1.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of the presently preferrednanoscale printing embodiments provided in accordance with practice ofthe present invention and is not intended to represent the only forms inwhich the present invention may be constructed or utilized. Thedescription sets forth the features and the steps for constructing andusing nanoscale ink-jet printing of the present invention in connectionwith the illustrated embodiments. It is to be understood, however, thatthe same or equivalent functions and structures may be accomplished bydifferent embodiments that are also intended to be encompassed withinthe spirit and scope of the invention. Also, as denoted elsewhereherein, like element numbers are intended to indicate like or similarelements or features.

The spatial resolution of ink-jet deposition is ultimately fixed by thesize of the nozzle through which the liquid stream emerges. The minimumsize of the nozzle is set by the volumetric flow rate of the liquidthrough the nozzle and thereby by the cross sectional area of the nozzleand viscosity of the liquid. Considering the case of simple Poiseuilleflow (viscous fluid flow through a long straight tube of circular crosssection), the volumetric flux Q is $\begin{matrix}{{Q = \frac{\pi\quad a^{4}\Delta\quad p}{8\quad\mu\quad l}},} & (1)\end{matrix}$

where a is the radius of the tube, I the length of the tube, Δp thepressure difference between the ends of the tube, and μ the viscosity ofthe fluid. Accordingly, the volumetric flux decreases dramatically asthe radius of the nozzle is decreased and increases as the viscosity ofthe fluid is decreased.

Conventional ink-jet printing can dispense droplets of diameter rangingfrom 15 to 200 μm (2 pl to 5 nl droplet volume) at rates of up to 25,000droplets/s for pulsed (on demand) operation or up to 1 milliondroplets/s for continuous flow operation. This droplet size rangeprovides more than adequate spatial resolution for printing purposes andeven suffices for some microfabrication applications such as DNAdeposition, chemical synthesis, biopolymer and solid supportapplications, chemical analysis, and microassembly of electronic orphotonic material.

However, when viscous materials are deposited or when higher throughputis desired, prior art ink-jet printing technology suffers from at leastseveral shortcomings. Among other things, for a given viscosity,generating significantly smaller droplets (i.e., by decrease in nozzlesize) for higher spatial resolution is not feasible without sacrificingthroughput. With reference to equation (1), the throughput of a 20 nmdiameter nozzle, for example, would be a factor of 10¹² less than thatof a 20 μm nozzle of the same length and at the same pressure drop.

Thus, by employing superfluid liquid helium as the “ink” medium, thethroughput limitation of equation (1) is removed due to the fact thatsuperfluid helium, by its nature, has zero viscosity. Thischaracteristic is well documented: Helium in the superfluid state is asecond liquid phase of Helium that appears at low temperatures below theliquid-solid transition pressure. Helium is the only material known todisplay superfluid behavior and the phenomenon is exhibited by bothstable isotopes of helium, ⁴He below approximately 2.2 ^(o) K, and ³Hebelow approximately 0.0025 ^(o) K. ⁴He is the much more abundant andinexpensive isotope. These properties, along with its higher superfluidtransition temperature, make ⁴He the preferred species for the variousink-jet uses described in this application. However, superfluid ³Hewould be entirely suitable at very low temperature for use with theembodiments provided in accordance with aspects of the presentinvention.

With zero viscosity, equation (1) would predict an infinite throughput.This, however, is disallowed by conservation of energy, since infinitethroughput of a fluid of finite mass would correspond to infinitekinetic energy. Therefore, conservation of energy becomes thecontrolling physical law, in the form of Bernoulli's Law. The flowvelocity v for a superfluid in horizontal flow then depends only on thedensity and the pressure difference, specifically $\begin{matrix}{{v = \sqrt{\frac{2\Delta\quad p}{\rho}}},} & (2)\end{matrix}$

where ρ is the mass density of the fluid. At pressure gradients of nearone atmosphere, equation (2) predicts flow velocities of a few tens ofmeters per second for superfluid helium. The corresponding volumetricflow rate through a circular channel of radius a is given by theequation $Q = {\pi\quad a^{2}\sqrt{\frac{2\Delta\quad p}{\rho}}}$

in which there is no dependence on the viscosity μ and in which thedependence on the channel radius a is only quadratic (rather thanquartic, as for Poiseuille flow). Hence, by utilizing superfluid heliumas the ink medium for ink-jet printing, print speed is much lessdiminished when attempting higher resolution printing since viscosity isno longer a factor and since throughput decreases much less rapidly withdecreasing channel radius.

Turning now to FIG. 1, a semi-schematic component diagram depicting acontinuous mode superfluid liquid helium jet apparatus (herein “jetapparatus”) for nanoscale ink-jet deposition provided in accordance withaspects of the present invention is shown, which is generally designated10. The jet apparatus 10 is capable of nanoscale printing droplet sizesof about 1 nm to about 999 nm. However, by selecting a larger orificesize, as further discussed below, the jet apparatus 10 may also printlarger droplet sizes. In one exemplary embodiment, the jet apparatus 10comprises a system having a housing 12, one or more chambers orcompartments 14 a, 14 b, 14 c, and components for propelling the helium,for controlling the helium, for optionally mixing or loading the helium,for depositing the helium onto a substrate, and for maintaining highvacuum as further discussed below.

In one exemplary embodiment, a cryostat 16 is incorporated and cooled tobelow the ⁴He superfluid transition temperature by the well-documentedtechnique of pumping on an enclosed volume of liquid ⁴He. A wide varietyof commercial bath cryostats is available for this purpose. Typicallythe cryostat 16 incorporates a liquid nitrogen cooled shroud (not shown)that encloses and thermally shields all helium-cooled portions of thecryostat. Situated within the nitrogen-cooled shroud in direct thermalcontact with the helium-cooled portion of the cryostat is a vessel 23,which is therefore at essentially the same temperature as the cryostathelium bath. This vessel 23 incorporates a nozzle 20 at one end thereofthrough which the ⁴He ink-jet issues. Filtered ultra-pure gaseous ⁴He isdelivered to the vessel 23 through a separate supply line 22 at a chosendelivery pressure. In one exemplary embodiment, filtration may beincorporated into the nozzle vessel 23 itself. Appropriate pressureregulation may be employed to set and regulate the pressure of the ⁴Hegas at a chosen pressure from about 0 atm up to about 25 atm. Thisgaseous helium condenses into a superfluid liquid as it passes throughthe vessel 23.

By virtue of its zero viscosity, the superfluid component of the liquidwithin the vessel 23 then issues from the nozzle 20 and into thesurrounding chamber 14 a as a cylindrical superfluid liquid free-jet. Toensure that cryogenically-cooled components of this free-jet do not heatexcessively, to prevent condensation of ambient gases onto the cryogenicsurfaces, and to allow unobstructed passage of the superfluid free-jet,the housing 12 and the various chambers within the housing are held in avacuum environment, typically 10⁻⁸ atm or less but ranging up to 10⁻³atm or higher in certain applications. Apart from the cryostat sectionthat houses the superfluid helium ink-jet nozzle, all components of theapparatus 10 may be kept at or near room temperature with fluctuationsbeing acceptable.

In one exemplary embodiment, the nozzle 20 may be fabricated in avariety of ways to produce an aperture ranging from 1 nanometer up toseveral hundred thousand nanometers in diameter. Exemplary fabricationmethods include the ion milling of holes through thin plates and thepulling of glass or quartz capillary tubes using commercially availableapparatus. Small apertures in plates and microcapillary nozzles are bothcommercially available. Although not deemed necessary for theunderstanding of the present invention, additional information may befound in the Rev. Sci. Instrum. 68, 3001-3009 (1997) publication underthe article entitled “Micrometer-sized nozzles and skimmers for theproduction of supersonic He atom beams,” authored by J. Braun, P. K.Day, J. P. Toennies, G. Witte, and E. Neher, the content of which isexpressly incorporated herein by reference, The cylindrical superfluidjet issuing from the nozzle orifice has approximately the same diameteras the orifice itself. The orifice diameter therefore determines thesize of the free-jet superfluid beam.

Because of a phenomenon known as Rayleigh instability, the cylindricalfluid beam of helium issuing from the nozzle 20 breaks up intomonodispersed droplets 24. To narrow the droplet size distribution andto phase lock droplet formation to a fixed frequency, a disturbancefrequency (which may either be a single fixed frequency to produce a setdroplet size or a variable frequency to fine-tune the droplet size) maybe imparted to the fluid at the nozzle 20 to create pressure,temperature, or entropy oscillations in the superfluid stream. Thenozzle 20 is an equivalent of a print head in an ink-jet printer and incertain embodiments may comprise a plurality of nozzles 20.

In one exemplary embodiment, an electromechanical device, also referredto as a Rayleigh instability driver, which may include a piezoelectrictransducer or a speaker 26 and associated electronic control unit 28, isused to impart pressure, temperature, and entropy oscillations to thenozzle 20. When implemented, an electronic control unit 28 supplies aperiodic voltage to drive the transducer device 26 at a desiredfrequency. In this manner the production of droplets is phase-locked tothe electronic drive signal of the electronic control unit. Theelectromechanical device 26 and its associated control unit 28 may beone of several commercially available instability drivers controlled bya system control computer (not shown) to regulate the size and amount ofdroplets 24 issuing from the nozzle 20.

A charging apparatus 30 controlled by a charge driver 32 comprising oneor more electrodes for imparting electric charges to the droplets 24 maybe incorporated in the jet apparatus 10 of the present embodiment. Whenimplemented, the charging apparatus 30 imparts an electric charge toissuing droplets 24 so that the charged droplets 24 may be manipulateddownstream in a deflection field (not shown). The deflection fieldoperates by creating a charged field to either attract or repel acharged droplet 24 as the droplet passes through the field to produce adesired droplet deflection. For example, the deflection field candeflect a charged droplet to an overflow chamber for recycling thedroplet or can allow the droplet to continue its path towards thedeposition chamber 14 c. In one exemplary embodiment, the charge driver32 and the deflection field receive character data input for a desireddroplet deposition, which then carry out the function by either allowingthe charged droplets 24 to travel to the third chamber 14 c fordepositing onto a substrate or to an overflow chamber for recycling.This deflection scheme is conventional in the microscale ink-jettechnology.

In one exemplary embodiment, a deflector 34 made by MEMS microfabrication techniques may be incorporated inline with the issuingdroplets 24 to vary the frequency or cycle of droplets 24 that depositonto a substrate 33. The deflector 34 may be used instead of or inaddition to the combination charging apparatus 30 and deflection fielddiscussed above. For example, the droplets 24 may issue from the nozzle20 at a rate of 100,000 drops per second and the deflector 34 is used toobstruct the path of the droplets to vary the number of drops thattravel to the second chamber 14 b and then to the third chamber 14 c toanywhere from between 0 to 100,000 drops per second. The deflector 34may be tied to a deflection driver 36 for controlling the rate ofdeflection of the issued droplets. Deflected droplets 35 deflected bythe deflector 34 may be educted away, scrubbed or filtered, and thenrecycled back into the ink supply reservoir 16 for reuse.

In one exemplary embodiment, after the droplets 24 travel pass the firstchamber 14 a, they enter the second chamber 14 b (herein alternativelyreferred to as “pickup chamber”). The second chamber 14 b is alsomaintained in a vacuum or near vacuum condition similar to the firstchamber 14 a. The second chamber 14 b may include one or more dopant-jetinjectors (three shown) 38 a, 38 b, 38 c with each jet assemblyconnected to a sample source (not shown) containing liquids (herein“dopants”) to be deposited with nanoscale resolution onto the substrate33. In exemplary embodiments, these dopant liquids might be bioactivemolecules, biomedical reagents, DNA samples, polymers, antibodies,proteins, genes, viruses or the like. The dopant-jet injectors 38 a, 38b, 38 c are configured to controllably release the dopants via injectordriver control electronics (not shown) for injection into the secondchamber 14 b. Once deposited in the second chamber 14 b, the individualdopant atoms/molecules collide with and are incorporated into thesuperfluid ⁴He droplets 24. The helium droplets with the entraineddopant atoms/molecules 40 then travel to the deposition chamber or thirdchamber 14 c for deposition onto the substrate 33. In one exemplaryembodiment, the dopant-jet injectors 38 a, 38 b, 38 c may comprise anozzle, a combination of a nozzle and a valve, an eductor andcontroller, or other conventional means for discharging a stream of gasor fluid.

In an alternative embodiment, dopant atoms or molecules are mixed intothe helium gas before it enters the source vessel 23 through the supplytube 22. This gas mixture condenses into a liquid mixture as it passesthrough the source vessel to issue from the nozzle as a superfluidstream with the dopant species already entrained. Break-up of the liquidfree-jet into droplets proceeds due to Rayleigh instability as in thecase of pure helium, leading to dopant containing droplets as in thatcase. Since the presence of dopants within the source vessel 23 caneasily lead to blockage of a nanoscale nozzle aperture, this embodimentshould be limited to dopant species that neither coagulate within theliquid mixture nor attach to the wall of the of the nozzle vessel atsuperfluid temperatures.

The dopant-jet injectors 38 a, 38 b, 38 c may be synchronized with thesuperfluid beam or droplets 24 to deliver a pulse of gas at some desiredamount and frequency. In one exemplary embodiment, the synchronizationis accomplished by phase-locking the dopant-jet injectors to dropletproduction controlled by the electromechanical device 26 and electroniccontrol unit 28 discussed above. Preferably, the dopant-jet injectorsare aimed in the direction of the superfluid beam path and areconfigured to discharge at some predetermined sequence or pattern at themoment that the droplets pass through the second chamber 14 c. If acharging apparatus 30 and a deflection field are used instead of thedeflector 34, then a continuous steam of droplets 24 will pass throughto the second chamber 14 b. In such configuration, the dopant-jetinjectors 38 a, 38 b, 38 c, should be synchronized to only generate apulse of gas dopants for a droplet destined for the third chamber 14 c.Commercial pulsed molecular beam nozzles may be used to inject thedopant species into the pickup chamber 14 b. Each pulsed nozzle ordopant-jet injector is preferably supplied with a particular dopantatom/molecule, either as a pure gas or as a dilute mixture of the dopantspecies in an inert carrier gas. A wide variety of techniques isavailable for non-destructively volatilizing and injecting atomic andmolecular species through pulsed molecular beam nozzles, includingcomplex molecular species, bioactive species, species of high molecularmass and species of low vapor pressure.

In an alternative exemplary embodiment, only one species of dopant isutilized with the jet apparatus 10 for deposition onto a substrate. Thesingle dopant species is preferably volatile at room temperature or canbe made so by mild heating of an enclosed vessel containing the dopant.By allowing the dopant gas to flow slowly into the pick-up chamber 14 bthrough appropriate interconnecting tubing and through arate-controlling aperture or valve, a steady-state low backgrounddensity of the dopant species can be maintained within the pick-upchamber. The superfluid helium droplets 24 in passing through the pickupchamber 14 b will collide with and capture the dopant atoms/moleculesdirectly from the ambient background gas, thus eliminating the need fordopant injector nozzles. The background gas pressure of the dopantspecies is adjusted by choice of the rate controlling valve or aperturethrough which it enters the pick-up chamber, thus allowing a desirednumber of the dopant atoms/molecules to be picked up by each superfluiddroplet in its passage through the pickup chamber.

A helium droplet 24 passing through the pickup chamber 14 b has a finiteprobability of colliding with a dopant atom/molecule or atoms/moleculesreleased by one or more of the dopant-jet injectors 38 a, 38 b, 38 c.Collision of a helium droplet with a dopant molecule results in thecapture of and incorporation of the dopant species into the superfluidhelium droplet A helium droplet with one or more entrained dopantspecies is also referred to herein as a loaded droplet. The probabilityof collision scales directly with the density of dopant atoms/moleculesalong the path of the helium droplet stream. Consequently, the averagenumber of dopant collisions experienced by a superfluid droplet in itstransit through the pickup chamber 14 b, and therefore the number ofdopant atoms/molecules it captures during this transit, can becontrolled by adjusting the density of the injected molecules along theaxis of the droplet beam. Studies have confirmed that superfluid heliumdroplets may be loaded in this fashion with a wide variety of dopantspecies including as specific molecule samples SF₆, OCS, and C₂H₂O₂. Inaddition, studies have shown that foreign molecules will eitheraggregate at the center of the helium droplets or will decorate thedroplets'exterior surface depending on the molecule-helium interaction.Molecules that aggregate at the center of the droplets are preferred,although dopant species exhibiting external decoration are also usablewith the present embodiment.

The directed stream of superfluid droplets, loaded with dopantatoms/molecules 40, exits the pickup chamber 14 b through a smalldiameter collimating aperture 42. If this collimator has the shape of atruncated cone with a sharp leading edge, it is also referred to as a“skimmer.” A skimmer of micro- or nano-sized aperture is referred to asa microskimmer or nanoskimmer, respectively. This prescribed shape ofthe skimmer leads to improved transmission of the helium beam throughthe collimating aperture, although in many instances a collimatingaperture having the form of a simple aperture in a flat plate may alsosuffice. Skimmers of the prescribed form may be fabricated by the sametechniques described above for forming nanoscale nozzles frommicrocapillary tubing.

One purpose of the skimmer or collimator is to minimize effusion ofdopant atoms from the pickup chamber 14 b into the deposition chamber 14c. The highly directed stream of superfluid helium droplets 40 passesunhindered through the collimator orifice. In contrast to this directedstream of dopant-loaded He droplets 40, any effusing molecules from theresidual gas in the pickup chamber will arrive at the collimator 42opening from all angles. Given the micro or nanoscale diameter of thecollimator 42 orifice, the flow of these residual gas species throughthe collimator orifice will be distributed over a range of angles andwill therefore have a very low intensity at the deposition surface inthe next chamber, 14 c. As a result, the collimator 42 essentiallyeliminates the flux of background atoms/molecules that travel from thepickup chamber 14 c into the deposition chamber 14 b.

Momentum is conserved in the collision of a droplet with a dopant atomor molecule. Consequently, the direction and speed of the dropletchanges slightly in the course of each collision. If this deflection isknown, as is the case when both the droplet and the dopant are travelingat a known speed and in a known direction prior to the collision, theresulting deflection can be employed to precisely select loaded heliumdroplets according to the number of dopant molecules contained withineach. In this instance the collimator 42 is mounted such that itsspatial position can be varied in situ, allowing its position to bevaried such that only loaded droplets with a specified number of dopantatoms or molecules pass from the pick-up chamber 14 b into thedeposition chamber 14 c.

A translational assembly 44 comprising a print platform 46 for mountingthe substrate 33 is positioned in the deposition chamber 14 c. In oneexemplary embodiment, the print platform 46, which may be a plate, aroller, or a rotating platform, is configured to translate in the X-Y-Zdirections by a plurality of stepper motors or DC motors (not shown),similar to stepper motors and DC motors used with existing ink-jetprinters. The rotating platform, if employed, may embody a tape chart orstrip chart. Alternatively, if ink depth or deposition depth is notdesired, the print platform 46 may be supported and translated along theX-Y directions only. The translational assembly 44 allows patterns orcharacters to be printed onto the substrate 33 by moving the substraterelative to the nozzle 20 so that the point of impact of the pickupdroplets 40 onto the substrate varies to create a desired pattern orimage. Three dimensional depositions may be found in tissue engineeringwhere, for example, biosorbable polymers are printed to form scaffoldsin the desired tissue shape.

When a pickup droplet 40 with foreign molecules aggregated at the centerof the helium droplets impacts the substrate 33, the helium sheathsurrounding the aggregated molecules provides an intrinsic impactcushion so that the molecules experience a slow and controlleddeceleration as they impact the surface 33. This is also referred to asa “soft landing.” By controlling the helium droplet size, more or lesscushion may be provided for the impacting molecules. In one exemplaryembodiment, the helium droplet size may be controlled by varying orcontrolling the orifice size of the nozzle 20. The helium droplet shouldbe sized with sufficient dimension to decelerate the aggregatedmolecules to near-zero velocity before impacting the substrate 33.

This “soft landing” process brings the dopant atoms/molecules intophysical contact with the process surface while leaving them with littlekinetic energy, thus allowing them to efficiently bind to the surface ofthe substrate through physisorption or chemisorption. Helium-mediatedsoft landing, by virtue of the inert and non-destructive nature ofhelium, is amenable to use with any type of surface or thin film,including those of both inorganic materials (metals, semiconductors, andinsulators) as well as organic materials. Exemplary surfaces or thisfilms would be those used in the semiconductor processing industry andMEMS industry as well as those proposed for use in molecular electronicsand biological sensor technologies. With provisions for cooling thesubstrate surface to a low operating temperature, even very non-reactivespecies can be made to physisorb. However, many dopant species can beexpected to bind strongly at room temperature.

Helium is extremely inert and also has the lowest boiling point (4.2 oK)of any atom or molecule. Accordingly, during deposition of the dopants,the helium carrier gas should not bind to the substrate surface at anytemperature appreciably in excess of 4.2 oK. Instead, He will return toits gas phase, which can then be evacuated out of the deposition chamber14 c by one or more vacuum pumps and can be collected, purified, andrecycled if desired.

For dopant atoms or molecules that decorate the exterior surface of thehelium droplets rather than aggregating at the center, a sacrificiallayer of inert gas, such as argon, could be deposited on the substrate33 to provide the soft or cushioned landing. The sacrificial layer maybe deposited by lowering the substrate 33 to a sufficiently lowtemperature to facilitate absorption of the inert gas. Then by admittinga sufficient quantity of the inert gas to the deposition chamber, anadsorbed layer of a chosen thickness will develop. The remaining gas orexcess gas may then be pumped out of the deposition chamber 14 c andrecycled if desired. The nanoscale printing can commence by activatingthe helium beam and carrying out the deposition process along the linesdescribed above but with the deceleration mediated primarily by theadsorbed layer of inert gas on the substrate surface rather than thehelium sheath of the impinging droplet. In the alternative embodimentthat uses a layer of cushion of inert gas, the translational assembly 44is preferably temperature controlled.

In one exemplary embodiment, the nozzle 14 a, pickup 14 b, anddeposition 14 c chambers are configured with appropriate vacuum pumpingor educting capability to remove background or excess gases and maintainconditions of sufficiently low pressure that any residual gasesremaining within those chambers do not adversely affect the depositionprocess, either through contamination or deflection of the loadedink-jet droplets or through contamination or deterioration of thesubstrate or of the nanostructures deposited thereon. In one exemplaryembodiment, a vacuum of about 10⁻⁸ atm or less is preferred, althoughother vacuum for other conditions, such as operating temperature, dopantspecies type, etc., may also be used. A number of commercially availablevacuum pumps, vacuum control devices, and vacuum measuring devices areuseable with the jet apparatus 10 of the present invention to produce,maintain, and quantify vacuum conditions. Exemplary devices includethose used in the semiconductor processing industry.

In one exemplary embodiment, spent gases (i.e., gases not deposited ontothe substrate) may be pumped from the vacuum chambers 14 a, 14 b, 14 cand passed through a cold filter to purify the helium. This exhaust gaswill contain species other than helium, e.g. molecules of the dopantspecies that were not captured by a passing helium droplet. Given thevery low boiling point of helium, all species other than helium can bemade to condense or solidify upon passage through a sufficiently coldfilter. Subsequently, the helium may be further purified andre-liquefied by standard techniques.

Turning now to FIG. 2, there is shown a semi-schematic block diagram 54depicting an exemplary control system provided in accordance withaspects of the present invention. The block diagram 54 includes acomputer controller 56 for controlling various the jet apparatus 10functions. In one exemplary embodiment, the computer controller 56 maycomprise a computer coupled to a plurality of device drivers 58. Thedevice drivers 58 may include drivers for controlling the X-Y-Zdirections of the translational assembly 44, for controlling the printhead 60, which includes controlling the nozzle 20, the chargingapparatus 30, and the other components implemented with the jetapparatus 10 for controlling the deposition of molecules onto thesubstrate 33. In addition, the one or more device drivers may be used tocontrol the operating parameters of the cryogenic source 16 and thedopants. Other operating parameters include controlling the vacuum inthe housing 12, the temperature of the translational assembly 44, andthe position of the collimator or skimmer 44.

An image collector 62 may be included and controlled by the computercontroller 56. The image collector 62 may include a video recorder or acamera or both for collecting footages and still images of patternsdeposited on the substrate 33. The image collector 62 may include bothmanual and automatic mode for capturing images and footages. In oneexemplary embodiment, images may be formed by directing electromagneticwaves, electrons, ions, or neutral atoms/molecules against thedeposition surface.

An exemplary microscale ink-jet printer for depositing biologicallyactive materials and the like is commercially available by MicroFabTechnologies, Inc., Piano, Tex., under the trademark JETLAB®. TheJETLAB® printer is available in both a continuous mode (similar to themode described above) and a print on demand mode, similar to existingbubble jet or ink-jet printers. The present embodiments may be practicedby modifying the JETLAB® printer to operate as described above, namelyto operate with superfluid helium as the ink diluent, to deposit dopantsfor pickup by helium droplets, and to deposit dopants onto a substratethrough non-direct-contact printing technique.

Although the preferred embodiments of the invention have been describedwith some specificity, the description and drawings set forth herein arenot intended to be delimiting, and persons of ordinary skill in the artwill understand that various modifications may be made to theembodiments discussed herein without departing from the scope of theinvention, and all such changes and modifications are intended to beencompassed within the appended claims. Various changes to the jetapparatus may be made including the use of nanoscale nozzle aperturesformed by means other than ion milling or microcapillary pulling;variations in the size, shape, and construction of the apparatuschambers; the type and pumping speed of the vacuum pumps, gauges, andassociated electronics; the method of cooling the helium liquid to itssuperfluid state; the type, number, means of activation, and control ofdevices used to inject dopant atoms/molecules into the path of thesuperfluid droplets; the use of molecular filters (e.g. electrophoresis)to supply the dopant injectors with a dopant species flow that varies inflow rate and/or species type and concentration as a function of time;the use of a pulsed liquid helium free-jet nozzle rather than acontinuous flow nozzle; the orientation of the superfluid free-jet to behorizontal, vertical, or at any angle in between these extremes; thegravitational deceleration to lower or zero velocity of avertically-oriented superfluid free-jet; the control of deposition bymoving the nozzle relative to a stationary substrate rather than viceversa or by moving both; the scattering of the superfluid droplets fromsurfaces or neutral molecular beam optical elements (e.g. diffractiongratings) in order to manipulate the beam trajectory and/or the dropletcharacteristics; the use of neutral molecular beam optical elements tofocus or defocus the superfluid beam; the deflection and manipulation ofthe superfluid droplets via momentum and/or energy transfer throughimpact with other molecular beams; and the reaction and/or combinationof one or more dopant species within the superfluid droplets for thepurpose of creating novel dopant species within the droplets prior todeposition. Accordingly, many alterations and modifications may be madeby those having ordinary skill in the art without deviating from thespirit and scope of the invention.

1. A jet apparatus for nanoscale printing onto a substrate comprising aprint head and a translational apparatus housed in a housing comprisingat least one housing chamber; a reservoir comprising a cryogenic fluidin communication with the print head; and a dopant injector mechanicallycoupled to a storage containment comprising dopant molecules; andwherein at least one droplet of the cryogenic fluid is discharged fromthe print head and is expelled across at least a part of the housingchamber to combine with at least one dopant molecule discharged from thedopant injector, and wherein the combined at least one droplet of thecryogenic fluid and the at least one dopant molecule collides with thesubstrate positioned on the translational apparatus.
 2. The jetapparatus of claim 1, further comprising an electrical-mechanicaldevice; wherein the electrical-mechanical device induces an oscillationonto the print head.
 3. The jet apparatus of claim 1, further comprisingan exhaust line in communication with the housing chamber and a vacuumpump in communication with the exhaust line.
 4. The jet apparatus ofclaim 1, further comprising a second dopant injector and a secondstorage containment comprising dopant molecules of a second type.
 5. Thejet apparatus of claim 1, further comprising a charging apparatus forcharging the cryogenic fluid issuing from the print head and adeflection field for changing direction of the charged cryogenic fluidissuing from the print head.
 6. The jet apparatus of claim 1, furthercomprising a MEMS deflector mounted inline with the print head fordeflecting the cryogenic fluid issuing from the print head.
 7. The jetapparatus of claim 1, further comprising a layer of inert gas formed onat least a portion of the substrate.
 8. The jet apparatus of claim 1,wherein the cryogenic fluid forms a carrier droplet and wherein the atleast one dopant molecule is absorbed into an interior of the carrierdroplet or is adsorbed onto an exterior of the carrier droplet.
 9. Thejet apparatus of claim 1, further comprising an image collector pointedat the substrate for collecting still or moving images of the substrate.10. The jet apparatus of claim 1, wherein the cryogenic fluid issuperfluid helium.
 11. The jet apparatus of claim 1, wherein the dopantmolecules comprise a biologically active material.
 12. The jet apparatusof claim 1, wherein the reservoir is part of a cryostat and wherein thecryostat is cooled to below a superfluid transition temperature of ⁴He.13. The jet apparatus of claim 1, further comprising a computercontroller and device drivers for controlling the print head and thedopant-jet injector.
 14. The jet apparatus of claim 1, wherein the printhead comprises a nozzle comprising an orifice having a diameter ofbetween about 1 nm to about 100,000 nm.
 15. The jet apparatus of claim1, further comprising a collimator mounted inline with a path of thecryogenic fluid.
 16. The jet apparatus of claim 1, further comprising atleast one stepper motor in mechanical communication with thetranslational apparatus.
 17. The jet apparatus of claim 2, wherein thedopant-jet injector is synchronized with the cryogenic fluid by phaselocking with the electrical-mechanical device.
 18. The jet apparatus ofclaim 3, wherein the vacuum pump maintains the housing at a pressureranging from below 10⁻¹¹ atm up to about 1 atm as dictated by the dopantmolecules and the substrate.
 19. The jet apparatus of claim 18, whereinexcess cryogenic fluid and biologically active materially are eductedfrom the housing by way of the exhaust line and either recycled forreuse or discarded.
 20. The jet apparatus of claim 10, wherein thesuperfluid helium is either ³He or ⁴He.
 21. The jet apparatus of claim11, wherein the biologically active material comprises an ester, acarbohydrate, a lipid, a protein, a chromophore, a nucleotide, an RNA, aDNA, a purine, a porphyrin, an amino acid, a peptide, an antibody, atoxin, an antitoxin, a virus, a retrovirus, a vitamin, a vaccine, anenzyme, a chromosome, a gene, a bacterium or a microbe.
 22. A printercapable of non-contacting nanoscale printing comprising a print headcomprising a nozzle having a nanoscale diameter orifice, a cryostatcomprising a chamber comprising superfluid helium in fluid communicationwith the print head, a housing comprising at least one chambercomprising dopant molecules; and a translational apparatus comprising asubstrate; wherein the superfluid helium issuing from the nozzle of theprint head breaks up into nanoscale droplets; and wherein one or morenanoscale droplets of superfluid helium each picks up at least onedopant molecule and delivers the at least one dopant molecule intocontact with the substrate.
 23. The printer of claim 22, furthercomprising an electrical mechanical device in mechanical communicationwith the print head for imparting pressure oscillations onto the printhead.
 24. The printer of claim 22, further comprising a dopant-jetinjector, a storage containment coupled to the dopant-jet injector, anddopant molecules contained within the storage containment; and whereinthe dopant molecules in the at least one chamber are discharged from thedopant-jet injector.
 25. The printer of claim 22, further comprising anexhaust line in communication with the at least one chamber and a vacuumpump in communication with the exhaust line.
 26. The printer of claim22, further comprising a charging apparatus for electrically chargingthe droplets issuing from the nozzle of the print head and a deflectionfield for changing the direction of the charged droplets.
 27. Theprinter of claim 22, further comprising a MEMS deflector mounted inlinewith the print head for deflecting the superfluid helium issuing fromthe print head.
 28. The printer of claim 22, further comprising a layerof inert gas formed on at least a portion of the substrate.
 29. Theprinter of claim 22, wherein the at least one dopant molecule picked upby each of the one or more nanoscale droplets of superfluid heliumaggregates at a center of each of the droplet or decorates an exteriorsurface of each of the droplets.
 30. The printer of claim 22, furthercomprising a computer controller and device drivers for controlling theprint head and the translational apparatus.
 31. The printer of claim 22,wherein the nozzle comprises a diameter of between about 1 nm to about100,000 nm.
 32. The printer of claim 22, further comprising a secondchamber and a third chamber, wherein the chamber defines a sourcechamber, the second chamber defines a pickup chamber, and the thirdchamber defines a deposition chamber.
 33. The printer of claim 24,wherein the dopant-jet injector is synchronized with the superfluidhelium issuing from the nozzle by phase locking with anelectrical-mechanical device mounted to the print head.
 34. The printerof claim 22, wherein the superfluid helium is either ³He or ⁴He.
 35. Amethod for non-contact printing onto a substrate comprising: issuing astream of superfluid helium from a nozzle along a path and allowing thestream to form into a plurality of nanoscale helium droplets; placingdopants in the path of the plurality of nanoscale helium droplets andallowing at least some of the droplets to pick up some of the dopantsplaced in the path of the droplets; and depositing the picked up dopantsby allowing the at least some of the droplets that picked up the dopantsto collide with the substrate.
 36. The method of claim 35, furthercomprising the step of moving the substrate relative to the nozzle. 37.The method of claim 35, further comprising the step of maintaining avacuum during pickup and depositing steps.
 38. The method of claim 35,further comprising the step of moving the nozzle relative to thesubstrate.
 39. A jet apparatus for nanoscale printing onto a substratecomprising a housing comprising a nozzle having a nanoscale orifice, achamber under a vacuum, a translational apparatus comprising asubstrate, and a cryostat comprising a cryogenic source, wherein atleast some of the cryogenic source issues from the nozzle and dispersesinto nanoscale droplets in the chamber, wherein at least some of thenanoscale droplets each comprises at least one dopant molecule picked upin the cryostat or picked up in the chamber, and wherein the picked upnanoscale droplets impact with the substrate.